摘要
华南新元古代中期（746-827Ma）双峰式（玄武岩-流纹岩）火山岩喷发于大陆板内裂谷环境。它们极有可能与导致Rodinia超大陆裂谷化-裂解的地幔柱（或超级地幔柱）活动有关。根据岩石地球化学数据，华南新元古代中期裂谷基性熔岩可以划分为高Ti／Y（HT，Ti／Y〉500）和低Ti／Y（LT，Ti／Y〈500）两个岩浆类型。HT熔岩又可进一步划分为HT1和HT2等两个亚类。HT1熔岩主要分部于华南中-西部裂谷盆地之中，总体上属于碱性玄武质岩浆系列；HT2和LT熔岩主要分布于华南中-东部裂谷盆地之中，总体上属于拉斑玄武质岩浆系列。元素和同位素数据表明，华南新元古代中期裂谷基性熔岩的化学变化不是由一个共同的母岩浆结晶分异作用所产生。华南中-西部地区裂谷基性熔岩的母岩浆经受了辉长岩质结晶分离作用，而华南中-东部地区裂谷基性熔岩的化学演化则是受控于单斜辉石（cpx）士橄榄石（01）结晶分离作用。各个双峰式火山岩系中，基性和酸性熔岩间为分异结晶关系。华南新元古代中期裂谷火山岩系极有可能是源于共同的地幔柱，该地幔柱组分的成分为：eNd（f）≈＋6，Mg#≈0．7，La／Nb≈0．7。华南新元古代中期裂谷基性熔岩存在空间上的地球化学变化：华南中一西部HT1熔岩的母岩浆，没有受到明显的大陆岩石圈混染，保存了鲜明的地幔柱信号；而大陆地壳或大陆岩石圈混染作用对于华南中-东部LT和HT2熔岩的形成则有着重要贡献。研究揭示，华南新元古代中期裂谷基性熔岩的母岩浆总体上产生于上涌地幔柱较深层位的石榴子石稳定区（深度：100～130km）。中-西部裂谷基性熔岩的母岩浆（碱性玄武质）产生于深度较大（～130km）、部分熔融程度较低（〈10％）的条件下，中-东部裂谷基性熔岩的母岩浆（拉斑玄武质）产生于深度稍浅（～100km）�
The mid-Neoproterozoic （746 - 827 Ma） bimodal （basalt-rhyolite） volcanic rocks from South China erupted in an intracontinental rift setting. They are most likely related to the so-called mantle plume （or superplume） that led to the rifting-breakup of the supercontinent Rodinia. On the basis of petrogeochemical data, the mid-Neoproterozoic rift-related basic lavas in South China can be classified into two types of magmas： high-Ti/Y （HT, Ti/Y〉500） and low-Ti/Y （LT, Ti/Y 〈 500）. The HT lavas can be further divided into two subtypes ： HT1 and HT2. The HT1 lavas are mainly distributed in central-western rift-related basins in South China and generally belong to the alkaline basaltic series; the HT2 and LT lavas are mainly distributed in central-eastern rift-related basins in South China and generally belong to the tholeiitic series. Elemental and isotopic data suggest that the chemical variation of the mid-Neoproterozoic rift-related basic lavas in South China cannot be explained by crystallization from a common parental magma. The parental magmas of central-western rift-related basic lavas in South China were subjected to gabbroic fractionation while the chemical evolution of the central-eastern rift-related basic lavas is controlled by a clinopyroxene （cpx） ＋ olivine （ol） fractionation. In each bimodal volcanic succession, there exists a differentiation crystallization relationship between basic and silicic lavas. The mid- Neoproterozoic rift-related volcanic rocks from South China most likely originated from a common mantle plume source with the components of εnd （t） ≈＋6, Mg#≈0. 7, and La/Nb ≈ 0. 7. Our data show that the spatial geochemical variations exist in the mid-Neoproterozoic rift-related basic lavas in South China. The parental magmas of HT1 lavas in central-western part of South China were not obviously contaminated by continental lithosphere, with the plume signals well preserved; whereas continental crustal or continental lithosphere contamination has
出处
《西北地质》
CAS
CSCD
2009年第1期1-33,共33页
Northwestern Geology
基金
中国地质调查局综合研究项目(1212010611804)
关键词
华南新元古代中期裂谷火山岩
地球化学
岩石成因
地幔柱
大陆岩石圈
地壳混染
mid-Neoproterozoic rift-related volcanic rocks in South China
geochemistry
petrogenesis
mantle plume
continental lithosphere
crustal contamination
